Yeah, I agree with some of the above posts. Galactic Civilizations would get a major benfit from a tiny tweak to the invasion system, namely:
1. Have only a percentage of the population willing to fight, that varies depending on cultural influence.
2. The remaining population comes with the newly conquered planet, but there is a possibility of unrest, rebellion, etc., the liklihood of which is affected by cultural influence, the size of the military garrision, perhaps your moral alignment, etc..
Someone above who said this was overdone in Civ IV. I don't understand, look at the world around us right now and human history! You can have a massive and powerful military, but still not be able to control even a small country with the unified (or mostly unified) consent of the people.
To me these two changes are no brainers. They make the game more realistic (since every battle doesn't desend into total genocide), they add great strategic depth, and it requries no *major* changes to the game (most of the work would just be play-testing the different background calculations).
I seriouslly hope this is improved in GalCiv II. (I haven't played GCII yet.)